The present invention relates to novel cyclohexylcyclohexene derivatives that are useful as electrooptic display materials.
Typical examples of liquid-crystal display cells include the dynamic scattering mode cell proposed by G. H. Heilmeier et al. in Appl. Phys. Letters, 13, 46 (1968), the field-effect mode cell proposed by M. Schadt et al. in Appl. Phys. Letters, 18, 127 (1971), and the quest-host mode cell proposed by G. H. Heilmeier et al. in Appl. Phys. Letters, 13, 91 (1968).
While various characteristics are required of liquid-crystal materials used in these liquid-crystal display cells, the most important one which must be shared by all display cells is that they have a nematic phase over a broad range of temperatures including room temperature. Many of the practically feasible liquid-crystal materials satisfying this requirement are usually prepared by mixing several or more components including a compound having a nematic phase at a temperature in the vicinity of room temperature and a compound having the nematic phase in the temperature range higher than room temperature. Many of such mixed liquid crystals commercially used today are at least required to have a nematic phase over the entire range of temperatures from -30.degree. C. to +65.degree. C. With the recent expansion in the fields of applications of liquid-crystal display cells, a need has arisen for the development of liquid-crystal materials in which the temperature range for the appearance of a nematic phase is extended to even higher levels. More recently, it has become necessary to develop a nematic liquid-crystal compound having a high N-I point, that is, temperature at which a transition occurs from nematic to isotropic liquid phase or vice versa.
To meet these needs, U.S. Pat. Nos. 4,422,951, 4,439,340 and 4,536,321, as well as European Patent Nos. 62,470 and 119,756 have proposed compounds such as 4-[4'(4"-substituted cyclohexyl)-cyclohexyl]substituted benzene that have N-I points around 200.degree. C. LIquid-crystal compounds having a nematic phase in an even higher temperature range are described in U.S. Pat. Nos. 4,472,293 and 4,477,369, as well as European Patent Nos. 84,974 and 99,099; the compounds proposed in these patents include 4,4'-bis(4-substituted phenyl)-bicyclohexane, 4-substitutedz-{4'-[4"-(4"-alkylcyclohexyl)cyclohexyl]cyclohexyl}benzene, 4-alkyl-4"-(4-halogenophenyl)-octadecahydro-p-terphenyl and 4-alkyl-4"(3,4-difuorophenyl)-octadecahydrop-terphenyl and have N-I points around 300.degree. C.
However, the compounds proposed in these prior patents suffer from the disadvantage that their C-N point (temperature at which a transition occurs from crystalline to nematic phase or vice versa) or S-N point (temperature at which a transition occurs from smectic to nematic phase or vice versa), which are the lower limits of the temperature range where a nematic phase occurs, are high.
If these compounds having high C-N or S-N points are added to nematic mixed liquid crystals which are commonly used in practice as host liquid crystals with a view to enhancing their N-I points, a crystalline or smectic phase will appear in the low-temperature range.